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Dye-sensitized solar cells

A dye-sensitized solar cell (also Grätzel cell, short: dye solar cell [DSSC, DSC]) ise a class of solar cells belonging to the group of thin film solar cells. It works similar to the photosynthesis of a green leaf: Based on a semiconductor formed between a photo-sensitized anode and an electrolyte, light can be transformed to electrical energy.

Dye-sensitized solar cell’s model: The green leaf’s photosynthesis

Photosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Hereby one molecule of the pigment chlorophyll absorbs one photon and loses one electron. The rate of energy capture by this process worldwide is immense: Approximately 100 terawatts, which is about six times larger than the power consumption of human civilization!

A dye-sensitized solar cell similar to photosynthesis: Sunlight passes through the transparent electrode into the dye layer where it can excite electrons. Thus, based on a semiconductor formed between a photo-sensitized anode and an electrolyte, light can be transformed to electrical energy.

Dye-sensitized solar cell – Working Principle

A the begining, the sensitizer absorbs a photon and an electron is transferred from S° to a higher lying energy level. The sensitizer is in the excited state S+. Dye excitation is followed by electron injection into the TiO2 and by dye re-charging via a redox electrolyte (mostly I-/I3-). Electrons are transported in the TiO2 nano-particles to the anode (front contact), which consists of a transparent conductive oxide layer (TCO). The contact to the redox electrolyte is made by a (catalyst-coated) cathode (back contact). The electron is then transferred to triiodide to yield iodide, which reduces the oxidized dye S+ to its original state S°.